Power take-offs of a tractor are used to operate attached implements. These power take-offs operate at a single speed which may be outside the desirable speed range of the implement. If so, the operating speed of the power take-off will be unsuitable. More recently, power take-off drop boxes have been designed to operate at either of two speeds. Such assemblies are based on a reversible mounting plate and an attached drive shaft as disclosed, for example, in U.S. Pat. Nos. 3,991,629 (Dearnley) and 3,513,712 (Zajichek et al).
In the Zajichek et al apparatus, first and second drive flanges are provided, each of which rotates at a different speed. A drive shaft is attached to a reversible adaptor flange which is attached by a plurality of bolts to either the first or second drive flange. There are two sets of bolt holes, one set located near the outer area of the adaptor flange and the other set located near the inner area of the adaptor flange. Because of deliberate misalignment of the two sets of bolt holes, it is impossible to insert all of the attachment bolts in the incorrect receiving holes. Nevertheless, it is possible to insert one of the bolts in the incorrect bolt receiving hole. This will, of course, result in some fracture damage to the apparatus if it is subsequently operated in such a condition.
In the Dearnley apparatus, two drive flanges are again provided together with a reversible adaptor flange. The drive flanges, however, are designed such that when specialized bolts of a correct length are used, they are of insufficient length to engage improper mating holes. Nevertheless, if bolts of incorrect length are used, they may engage both flanges which can also cause fracture of the apparatus when operated in such condition.